This invention relates to tamper-proof locking mechanisms for controls having a rotatable control shaft projecting outwardly from a body housing a control means. In one aspect, the invention relates to mechanisms for locking quarter turn valves, such as ball valves, butterfly valves and plug valves, in a fully open and/or a fully closed position.
In some fluid operations, it is essential that certain manually-operated control valves be maintained in either the full open or closed position during normal operation. For example, Occupational Safety and Health Administration regulations require that certain control valves in hydraulic and pneumatic systems to be positively locked in the open or closed position. Another example is fire protection sprinkler systems where the control valves must be fully open at all times to insure proper water flow in the event of an emergency.
When such valves are located in areas where there is a risk of intentional tampering or where they may be unintentionally closed, opened or otherwise mispositioned, a locking mechanism which reliably and positively locks the operating handle in a selected position is required. To be completely effective, the locking mechanism must not only prevent rotational movement of the operating handle, but also prevent the operating handle from being lifted off the stem, even though a nut or the like holding the handle on the valve stem has been removed.
U.S. Pat. No. 5,014,528 discloses a locking and latching mechanism for quarter turn valves including an operating handle which is rotated to move a valve member between open and closed positions. The locking mechanism includes a pair of circumferentially-spaced lugs on the boss at locations corresponding to open and closed valve positions. A slider, mounted on the intermediate portion of the handle for reciprocative movement between locked and unlocked positions, carries a latch element having an open portion for receiving the respective one of the lugs when the handle is either open or closed. The open portion of the latch element engages the side surfaces of the lugs to restrain rotational movement of the handle when the slider is in the locked position. The open portion also has a bottom wall for engaging the bottom surface of the lugs to restrain axial movement of the handle relative to the control shaft when the slider is in the locked position.
The slider can be held in the locked position by a locking member, such as a padlock, mounted in an aperture in the intermediate portion of the handle, adjacent the slider when it is in the locked position. When such a locking member is not installed, the slider is biased by gravity toward a locked position when the valve is oriented either so that the handle is slightly upwardly in the open or closed position or generally vertically upwardly in the open position. However, when the valve of necessity must be installed in another orientation, e.g., because of restrictions of space or system layout, so that the handle is pointing downwardly when in one position or the other, gravity tends to cause the slider to slide away from the locking position. When that occurs, the handle is free to be moved, through inadvertent contact or otherwise, to partially or fully open or close the valve.